This invention relates generally to improved concrete building units and further to a method and apparatus for precasting the same.
Precast concrete building units of various types are known for use in building construction. A principal advantage of such elements is a reduction in labor costs and time incurred in erecting a building structure. It is known to precast entire room units, entire wall units and various other building elements, in a wide variety of sizes and configurations. Each of these units has its own benefits and advantages, as well as its own disadvantages and drawbacks. Many require heavy capital outlay for costly manufacturing plant facilities, costs to bring the precast units from point of manufacture to the building site, additional reinforcing for extensive transportation and handling, and special on-site erecting equipment.
It is known, for example, in hotel/motel building construction to assemble an entire building in modular form piecing together complete room units having prefabricated integral walls, ceiling and floor. Such units are large and heavy, which requires costly forming and causes difficulties in manufacture, transportation and erection. The room size is fixed in accordance with the precast unit, so variation in room size requires variation in the size of the molded unit. The height of the unit necessitates the use of scaffolding or similar structure in casting the ceiling and special accommodation must be made in the forms to achieve the box-like, hollow structure. Also, when such units are placed side by side to create the building structure, the wall thickness between adjacent rooms is unnecessarily doubled.
The unitary box-like structures such as those described suffer from a lack of flexibility and versatility and are limited in the uses to which they may be put. In a hotel/motel or condominium construction, for example, utilizing precast complete room units, an entire building will require additional on-site pouring or precast units of other types in order to complete assembly, the modular room units being suitable only for use as the rooms.
U.S. Pat. No. 4,606,878 to Day et al., for example, shows a method and apparatus for constructing complete precast concrete modular building units which include a base slab, a roof, two sidewalls and one end wall formed in a single molding operation. The outer surfaces are fabricated using a collapsible outer form having sidewall and end wall plates pivotally connected to a rectangular base plate. The interior surfaces are formed using a retractable inner form having hydraulically positionable elements. The mold form is very costly and the resulting structure is large and heavy, and limited in the uses to which it can be put. Also, the internal mechanism requires a certain minimum degree of skill to ensure proper operation.
U.S. Pat. No. 4,178,343 to Rojo, Jr. discloses a method and apparatus for precasting building components in the form of vertical wall units by means of reusable separable mold forms that are wheelable and can be utilized on-site. The units of Rojo, Jr. are smaller and more versatile than the larger, complete units of Day et al. but, nevertheless, require considerable on-site labor and erection skill and the use of a multiplicity of other components during building assembly. And, because of their small size, the number of units needed is very high.
Copending U.S. patent application Ser. No. 07/558,858 describes an improved precast concrete building unit in the form of a partial room configuration, which is suitable for use in room construction, but which also offers great versatility and flexibility for use as other components in modular building construction. That unit, shown in FIG. 1, takes the form of a half-room having a U-shaped configuration with a generally planar, horizontally extending web, from opposite longitudinal edges of which project a pair of spaced, generally planar, vertically extending flanges or leg sections. The extremities of the flanges or legs are respectively provided with complementary male and female members which serve as interlocking shear keys when two identical such units are placed in leg-to-leg, inverted relationship to complete top and bottom halves of a room. The outside edges of each unit at the junctures of the web and flanges are formed with complementary alternating tabs and voids to provide means for interlocking the outside juncture edges of identical units placed in diagonally adjacent, web-to-web inverted relationship.
One method for simple on-site fabrication of such improved building unit is described in the '858 application. That method employs reusable molding apparatus in the form of a wheeled cart of uniform inverted U-shaped cross-section and having a pair of laterally-spaced, vertical outer sidewall plates hingedly attached at lower edges to outside edges of outwardly extending flanges of a mold bottom comprising a pair of laterally-spaced, lesser height, vertical inner sidewall plates joined at upper edges by a horizontal top plate. Though some provision is made for being able to vary the size of the molding apparatus, in general the apparatus is sized to match the dimensions of the desired building unit, and its flexibility for being reusable to produce similar units of differing dimensions is limited.